1. Field of the Invention
The present invention relates to semiconductor exposure equipment which irradiates a wafer with light passed through a design pattern in order to expose a photoresist on the wafer to the design pattern. More particularly, the present invention relates to a method of and apparatus for detecting the presence of particles on a wafer holder of the semiconductor equipment which supports the wafer, and to a method of determining whether the presence of such particles is significant enough to constitute a defect.
2. Description of the Related Art
Generally, when manufacturing semiconductor devices, photomasking is used to transfer a semiconductor design pattern onto a wafer. This is achieved by first depositing photoresist on a wafer. Then the wafer/resist combination is inserted into a mask aligner, which contains the optics, ultraviolet (UV) light source, and the circuit layer image contained on a mask or reticle, which is to be transferred to the resist film. The mask or reticle pattern image can be transferred to the wafer on a scale of one-to-one, or at a reduced scale using projection optics to focus and reduce the image.
The exposure equipment (mask aligner) also contains a wafer holder for mounting the wafer thereon. The wafer holder itself is disposed on a stage, with the stage being driven by a motor or other driving device. After the wafer is mounted on the wafer holder, the reticle and wafer are aligned by driving the stage. Then, the design pattern is transferred onto the photoresist of the wafer using a light source which irradiates the reticle, and a reduction projection lens through which the light is passed to the wafer.
It is common for registration tolerances in high density chips to be on the order of .+-.2000 .ANG.. The total exposure energy is the combination of light intensity and exposure time, which must be tightly controlled to assure proper image reproduction.
However, this exposure process is often carried out while particles inadvertently remain on the wafer holder beneath the wafer, which can not be detected by conventional methods. Because the exposure process is carried out repeatedly, an accumulation of particles on the stage often results in some malfunction of the exposure equipment. Accordingly, the particles may also cause a mass of defects in the final semiconductor devices or, at the every least, may adversely affect the production yield.